JPH0747291B2 - Cylinder hydraulic circuit of injection molding machine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an improvement of a hydraulic circuit for driving a reciprocating cylinder of an injection molding machine.

(Prior Art) Injection molding of plastic is performed by injecting a heated and melted plastic material into a mold by the pressure of an injection cylinder, and opening / closing (mold), injection, holding pressure, and weighing.
One process is performed continuously as one cycle. Opening and closing is the process of taking out the solidified plastic from the mold by the mold clamping cylinder and preparing to receive the next material. In the injection process, the molten material is injected into this mold by the pressure of the injection cylinder. . In the pressure holding step, the injected plastic is cooled and solidified while being pressurized.
Further, in the measuring process, the plastic material in the hopper is introduced into the heating cylinder by the rotation of the screw. At this time, the injection cylinder retreats due to the pressure of the plasticized plastic, but a back pressure is applied to the injection cylinder to limit the retreat speed. In the injection and pressure-holding process, the hydraulic pump is driven to continuously apply the hydraulic pressure to the injection cylinder.

(Problems to be Solved by the Invention) By the way, in the injection process, a large amount of high-pressure oil must be introduced into the injection cylinder for material injection, and the electric motor driving the hydraulic pump must have a capacity to withstand this load. I won't. On the other hand, in the pressure-holding step, since the plastic material filled in the mold is maintained in a pressed state, the electric motor needs to continuously apply a pressurizing torque, and a motor having high thermal durability is required. As a countermeasure against these problems, there is a device in which an accumulator and a check valve are provided in the circuit so that pressurization is maintained by the accumulated pressure of the accumulator. In this case, it is necessary to provide a pressure control valve between the accumulator and the tank, which opens only during the metering process, in order to secure the back pressure necessary to limit the backward movement speed of the cylinder during the metering process. However, this pressure control valve controls the retreat speed of the cylinder and has a problem that the structure is complicated and expensive.

It is an object of the present invention to solve the above problems and provide a hydraulic circuit that can efficiently drive a reciprocating cylinder.

(Means for Solving the Problems) The present invention relates to a hydraulic circuit of a reciprocating cylinder used in an injection molding machine for injecting and molding a plastic material into a mold, wherein a discharge circuit of a hydraulic pump is reciprocating. It is connected to one oil chamber of the cylinder, an accumulator is installed in this discharge circuit, and a valve device is installed to prevent backflow of pressure oil when the cylinder reciprocates and to allow backflow when the cylinder reciprocates. There is.

(Operation) In the forward stroke process of the cylinder, the hydraulic pump supplies pressure oil to the cylinder and simultaneously accumulates pressure in the accumulator. In the cylinder pressure maintaining step, the pressure accumulated in the accumulator is prevented by the valve device from escaping to the hydraulic pump side, and the pressurized state of the cylinder is maintained. In the cylinder returning process, pressure oil flows back to the hydraulic pump by the valve device, and back pressure is generated by the resistance of the pump driven by the backflow oil.

(Embodiment) FIG. 1 and FIG. 2 show a first embodiment of the present invention.

In FIG. 1, 1 is an injection cylinder, 2 is a hydraulic pump,
An electric motor 3 drives the hydraulic pump 2. The discharge port P ₁ of the hydraulic pump 2 is connected to an oil chamber P ₂ that drives the plunger 1A of the injection cylinder 1 to the injection side, and a normally open no-leak valve 4 and an accumulator 5 driven by a solenoid on this circuit.
And are inserted in series. Further, the oil chamber P ₃ provided on the opposite side of the oil chamber P ₂ with the plunger 1A interposed therebetween is connected to the suction port P _{4 of the} hydraulic pump 2.
Connecting. The discharge port P ₁ and the suction port P ₄ of the hydraulic pump 2 are reversible, and the hydraulic pump 2 is connected to the accumulator 6 via the drain port P ₅ . The accumulator 6 is connected between the discharge port P ₁ and the no-leak valve 4 via the check valve 7, and the suction port P ₄ and the oil chamber are connected via the check valve 8.
Connect to P ₃ . Further, a relief valve 9 is provided in parallel with the check valve 8 for allowing the working oil to flow from the suction port P ₄ toward the accumulator 6 under a certain pressure or more. The above configuration is unitized. The electric motor 3 that drives the hydraulic pump 2 and the no-leak valve 4 are controlled by a controller 10 outside the unit.

The injection cylinder 1 is provided with a screw, a heating cylinder, and a hopper (not shown) in the front (right direction in the drawing), and after melting the material supplied from the hopper with the heating cylinder, the nozzle at the tip of the heating cylinder enters the mold. To eject.

Next, the operation will be described with reference to FIG.

In the opening / closing process, the hydraulic pump 2 is not driven and the no-leak valve 4 is open in the OFF state. The hydraulic pump 2 up to the injection step operates to send high-pressure hydraulic oil to the oil chamber P ₂ of the injection cylinder 1, and at the same time, the accumulator 5 accumulates pressure. The hydraulic oil sent into the oil chamber P ₂ pushes the plunger 1A toward the injection side (the right side in the figure), thereby injecting the molten plastic material in the heating cylinder into the mold. Due to the displacement of the plunger 1A, the hydraulic oil in the oil chamber P ₃ is transferred to the hydraulic pump 2
Flows into the suction port P ₄ . In the pressure-holding process after injection, the no-leak valve 4 is switched on and closed through the controller 10, and the injection cylinder 1 presses and holds the plunger 1A toward the injection side by the pressure accumulated in the accumulator 5.
At this time, in order to decrease by hydraulic slightly due to leakage of pressure oil into the oil chamber P ₃ side, the motor 3 is activated via the controller 10 at some point, open the Noriku valve 4 and simultaneously drives the hydraulic pump 2 Accumulator 5 accumulates pressure again. When the accumulator 5 has sufficiently accumulated pressure, the no-leak valve 4 is closed and the operation of the electric motor 3 is stopped. Since this pressure accumulating work is performed at any time according to the pressure drop of the accumulator 5 during the pressure holding process, the oil chamber that presses the plunger 1A
The pressure of P ₂ is always maintained at a certain level or higher, and the electric motor 3 can be operated in a short time without the need for continuous operation. Next, in the measuring process, the leak valve 4 opens, and the oil chamber P ₂ and the accumulator 5
The hydraulic fluid flows back while rotating the hydraulic pump 2 due to the pressure. At this time, the plastic material is supplied to the heating cylinder and plasticized by the rotation of a screw (not shown).
Cylinder 1 by pressure f of plasticized plastic material
However, as a back pressure, a pressure due to the resistance of the hydraulic pump 2 rises in the oil chamber P ₂ , and the cylinder 1 is slowly pushed back. Therefore, the pressure in the accumulator 5 slightly rises as shown in FIG. 2, and the discharge port P _{1 of the} hydraulic pump 2 is increased.
Hydraulic fluid flows back from the suction port to the suction port P ₄ . As a result, the hydraulic circuit returns to the state of the first opening / closing process, and the next cycle is repeated.

Further, when the injection cylinder 1 is driven without supplying the plastic material for the purpose of a trial run or the like, the external force f does not act in the measuring process, so that the pressure in the oil chamber P ₃ is released after the pressure in the oil chamber P ₂ is released. Therefore, it is necessary to retract the plunger 1A.
At this time, the relief valve 9 to open at a predetermined pressure greater than the one helping retraction of plunger 1A to prevent the pressure of the oil chamber P ₃ side into the accumulator 6 can escape, the relief valve when the pressure is applied to the oil chamber P ₃ 9 prevents the plunger 1A from retreating suddenly and accumulates pressure in the accumulator 6. The accumulator 6 serves to compensate for changes in the amount of oil due to internal leaks, temperature changes, etc. in this closed hydraulic circuit.

FIGS. 3 and 4 show a second embodiment of the present invention, in which the configuration of the portion surrounded by the broken line in FIG. 1 is changed as shown in FIG. 3 to replace the no-leak valve 4 in front of the accumulator 5. A check valve with pilot 11 is provided. The check valve 11 is normally configured to allow only oil passage from the hydraulic pump 2 toward the injection cylinder 1 and allow oil passage in the opposite direction in the metering process. In the third embodiment of the present invention shown in FIGS. 5 and 6, the check valve 12 is provided upstream of the accumulator 5, and the no-leak valve 4 is provided in parallel therewith. In these second and third embodiments, the valve operation for guiding the accumulator 5 to the same operation as in FIG. 2 is simplified as shown in FIGS. 4 and 6, respectively.

7 and 8 show a fourth embodiment of the present invention. Here, the check valve 12 is provided upstream of the accumulator 5, the no-leak valve 4 is provided in series downstream, and another no-leak valve 13 is provided in parallel with these. In this embodiment, by closing the no-leak valve 4 and opening the no-leak valve 13 as shown in FIG. 8 during metering, the pressure of the accumulator 5 can be used for the next cycle without being released.

9 and 10 show a fifth embodiment of the present invention, which is an example applied to a mold clamping cylinder 1'of an injection molding machine. Here, the accumulator 5 is provided with a normally open no-leak valve 14, and a check valve 15 is provided in parallel with the no-leak valve 4 as a valve device interposed in the discharge circuit. These leak valves 4 and 14
Also, the electric motor 3 that drives the hydraulic pump 2 is controlled by the controller 10. 16 is the cylinder pressure (oil chamber
The pressure sensor detects the P pressure ₂₎ input to the controller 10, 17 is a stroke sensor for input to the controller 10 detects the stroke position of the plunger 1A. The mold clamping cylinder 1'operates in four cycles of mold closing, mold clamping, mold opening, and ejection as one cycle. The mold closing process is a process of driving the plunger 1A of the mold clamping cylinder 1'forward to close the mold. The controller 10 closes the no-leak valve 14, and the pressure oil from the hydraulic pump 2 leaks the check valve 15 and no-leak. It is supplied to the oil chamber P ₂ of the cylinder 1 ′ through the valve 4. As a result, the plunger 1A is pushed forward and the oil chamber P ₂ expands. At this time, since the accumulator 5 is shut off from the discharge circuit from the discharge port P ₁ to the oil chamber P ₂ by the no-leak valve 14, the high pressure stored in the accumulator 5 does not escape to the discharge circuit whose pressure is lower. Mold closing step the oil chamber P ₂ by a hydraulic fluid is supplied to the volume expansion of the oil chamber P ₂ stops to complete
The pressure rises rapidly, but this is detected by the output of the pressure sensor 16, and at the same time the cylinder stroke is detected by the stroke sensor 17, and based on this, the controller 10 closes the no-leak valve 4 and at the same time opens the no-leak valve 14 and at the same time, the electric motor 3 Stop driving. In this way, in the mold clamping process, the pressure accumulated in the accumulator 5 acts on the oil chamber P ₂ , and the controller 10 operates the electric motor 3 to drive the hydraulic pump 2 only when the pressure drops due to a leak of hydraulic oil. , Pressure oil is supplied to the oil chamber P ₂ and the accumulator 5. Since the pressure oil is supplied via the check valve 15, the operation of the no-leak valve 4 is not necessary and remains closed. In the next mold opening process, the no-leak valve 14 is closed, the no-leak valve 4 is opened, and the hydraulic pump 2 is rotated in the reverse direction via the electric motor 3. Along with this, the hydraulic oil flows in the direction opposite to the mold closing process, and the plunger 1A retracts. When the plunger 1A reaches a predetermined retracted position, the electric motor 3 is stopped by the controller 10 and the process proceeds to the take-out step in that state to take out the solidified plastic from the mold. During the period from the mold opening process to the next mold clamping process, the no-leak valve 14 shuts off the accumulator 5 from the discharge circuit and maintains the high pressure of the accumulator 5 until the next mold clamping process. This means that the driving period of the hydraulic pump 2 is shortened as compared with the first embodiment in which the pressure release of the accumulator 5 and the pressure accumulation are repeated every cycle, and therefore the hydraulic pump 2 and the electric motor 3 are further downsized. can do.

In the above, the first to fourth embodiments are intended for the injection cylinder, and the fifth embodiment is applied to the mold clamping cylinder.

(Effects of the Invention) As described above, the present invention includes the accumulator and the valve device that connects and disconnects the circuit between the hydraulic pump and the cylinder.
The hydraulic pressure stored in the accumulator can be used in the forward stroke of the cylinder, and the cylinder speed can be appropriately controlled by the rotational resistance of the hydraulic pump against the hydraulic oil flowing backward in the backward stroke. Therefore, the operating cost can be saved, and since the load time of the electric motor is short, there is little fear of overloading even when a full capacity load is applied, and the electric motor can be downsized accordingly, while the pressure control mechanism is omitted. The circuit configuration can be simplified.

[Brief description of drawings]

FIG. 1 is a hydraulic circuit diagram showing a first embodiment of the present invention, FIG. 2 is a timing chart showing an operating condition of the circuit, and FIG. 3 is a hydraulic circuit diagram of a main part showing a second embodiment. FIG. 5 is the same timing chart, FIG. 5 is a hydraulic circuit diagram of an essential part showing the third embodiment, and FIG.
FIG. 8 is a hydraulic circuit diagram showing the fourth embodiment, FIG. 8 is the same timing chart, FIG. 9 is a hydraulic circuit diagram showing the fifth embodiment, and FIG. 10 is the same timing chart. 1 …… Injection cylinder, 2 …… Hydraulic pump, 4,14 …… No leak valve, 5,16 …… Accumulator, 10 …… Controller, 15 …… Check valve.

Claims (1)

[Claims] 1. In a hydraulic circuit of a reciprocating cylinder used in an injection molding machine for injecting and molding a plastic material into a mold, a discharge circuit of a hydraulic pump is connected to one oil chamber of the reciprocating cylinder. A cylinder of an injection molding machine, characterized in that an accumulator is provided in the discharge circuit, and a valve device for preventing backflow of pressure oil when the cylinder reciprocates and for allowing backflow when the cylinder reciprocates. Hydraulic circuit.